Controlling apparatus for electric motors.



J. D. IHLDERQ CONTROLLING APPARATUS FOR ELECTRIC MOTORS.

APPLIOATION FILED DEC. 6, 1907.

Patented June 4, 1912.

a SHEETS-SHEET 1.

ATTORNEY J. D. IHLDER. CONTROLLING APPARATUS FOR ELECTRIC MOTORS.

APPLICATION FILED DEO.6, 1907.

1,028,731 Patented June 4, 1912.

' a SHEETSSHEET 2. i l -i I I 2 E' k a Q WHNESSES: I INVENTOR AM 1%. 01% BY M ATTORNEY APPLICATION FILED DBO. 6, 1907.

Patented June 4, 1912.

3 SHEETS-SHEET 3.

WITNESS-ES:

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30331? D. IHLDER, OF NEVT YORK, N. Y., ASSIGNGR TO OTIS ELEVATOR COMPANY, 013 JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

, con rnonnnve arrenlirus nos. nnncrnic Morons.

Specification of Letters Patent.

Application filed December 6, 1907.

Patented June 4, 1912. Serial No. 405,349.

and State of New York, have invented a new and useful Improvement in Controlling Apparatus for Electric Motors, of which the following is a specification.

My invention relates to controlling devices for electric motors, and is an improvement on the apparatus disclosed in my Patent No. 851,239, granted April 23, 1907, for an improvement .in controlling devices for electric motors.

The object of my invention is tosimplify and render more efficient the operation of electric motors.

" nieiits being Other objects of the invention will appear iereinafter, the novel combinations of eleset forth in the appended claims.

In the accompanying drawings, Figure l is a diagrammatic view showing the appli-. cation of my invention to the control of an electric motor, and comprises an electric switch operated by a single doubly wound magnet to control the motor circuit directly, and a brake magnet cooperating with said switch; Fig. 2 represents diagrammatically a similar view, but comprises two doubly wound magnets, one for controlling the motor circuit directly, and the other for controlling an extra field and an electrodyiiamic brake circuit; Fig. 3 includes a magnet having a single winding connected directly across the armature, said magnet operating a switch to control'the electrodynamic brake circuit and the extra field circuit; Fig. 4; is a View similar to Fig. 2, in that a brake magnet and two doubly wound controlling magnets are shown, but

variations in connections of the respective windings of the controlling electro magnets are illustrated; and Fig. 5 represents a brake apparatus in combination with an electromagnetic main line switch, which in turn is controlled by an auxiliary magnetic switch comprising a doubly wound electromagnet. Similar parts in all the views are designated by similar reference signs.

In the operation of electric motors which are required to operate under frequently varying conditions of load, as, for instance,

in, the special field of electric elevatoiis, the" motor sometimes attains an undue or excessive speed. This is particularly true in the case of motors employed in electric ele-.

vat-or service when the motor is driven by the load, and thereby becomes a generator.

It is among the special purposes of my invention to provide means which 'are simple, efficient and automatic in operation for imposing a retarding and a stopping influencc upon the motor. This object may be accomplished in many different ways, as by applying an electro-dynamic brake to the motor, by strengthening the magnetic field of the motor, or by breaking the motor circuit and applying a mechanical brake, or by combining these several methods, and in carrying out my invention 1' purpose to provide means operated automatically when the motor attains an undue or excessive speed for accomplishing the objects and purposes stated.

It is obvious that my invention may be applied to many ditferent'styles and types of motors and accessorydevices for start ing, stopping, reversing and controlling the motor. While, therefore, I have selected for the purpose of illustration a certain type .or motor and controlling devices therefor, I desire it to be understood that my invention is not to be limited or restricted thereto,

as variations therefrom and changes therein would readily suggest themselves to persons skilled in the art without departure from the spirit and scope of my invention, and without affecting the objects and purposes attained by my invention or the cooperative operation thereof.

in the several views of the accompanying drawings, designates a, motor, 21 the armature thereof, 22, 23 its brushes, 50 a seriesfield winding, a sectional starting resistance in circuit with the series field winding, and 100 designates the shunt field winding.

Any suitable construction and arrangement may be employed for successively cutting out or short-circuiting step by step the sectionalresistance 40 and the series field coils as the motor accelerates in speed. I have selected for purposes of illustration one form of mechanism for accomplishing this result, to which, however, my invention is not to be limited or restricted. This mechanism comprises the magnet 30, the winding or coil 31 of which is included in led starting resistance 40 and the series field coil 50, as, for instance, by successively attracting the contacts '39, 38, 37 and 36 to the contacts 35, 34:, 33, 32, respectively, in a well understood manner.

Any suitable form of construction and arrangement of starting, stopping and reversing switches may be employed for controlling the motor. While, therefore, I have selected for purposes of illustration a simple construction of switches,.which in practice is well adapted for the purpose, I desire it to be understood that my invention is in no wise to be limited or restricted to the form shown.

A simple starting and stopping switch is shown at 10 and comprises a movable member or switch lever 12 provided with an operating handle 11 and arranged to be brought into contact with' either one or the other of the cooperating contacts 13, 14.

The contact-maker 12 is connected to the positive main 7 through the conductor 16 and the switch comprising the contacts 68 and 69'.

The solenoids 91' and 92 are respectively included in circuit with the switch 10 through the conductor 95 on one side and the conductors '18 and 17 on the other, the conductor 95 being connected to the negative main 5. The solenoids 91, 92 by acting on their cores or plungers 89 and 90, respectively, control a reversing switch which, as above'indicated, may be of any form or construction. ln-the form selected for purposes oi illustration, thisswitch comprises a lever 80 pivoted as at 81, to which are connected as at 88 the plungers 89 and 90 so that said lever may be rocked or swung in one direction or the other, according as one or the other of the solenoids 91, 92 receives current. The lever 80 includes suitably insulated conducting parts 82, 83. The part 82 operates to bridge the fixed contacts 87, 56 when the lever 80 is rocked in one direction, and to bridge contacts 77, 55 when said lever is rocked in the other direction. Similarly, part 83 serves to bridge contacts 85, 86 or 84, 78, according to the direction in which lever 80 is rocked. Contacts 85, 84"

are connected together electricallyv and also to the positive main 7 through the conductor 7, contacts 68', 68, 67, 69. The contavs 7 7 and 86 are electrically connected to ether and through conductor 25. to the motor brush 23; while contacts 7 8 and 87 are electrically connected together and through conductor.

26 to the motor brush 22; The contacts 56, 55 are electrically connected together and The parts so far described and referred I to andas above indicated may be of any suitable construction and arrangement, the specific construction and arrangement of the details thereof per se are not of my invention, being selected merely for the purposes of illustration, and as showing constructions and arrangements-which are practicable and efiicient in operation and cooperation with my invention. In carrying out my invention and in associating the same with the motor and accessory devices of the general nature above referred to and as indicated, I purpose to provide means whereby the motor may be automatically slowed down and positively stopped upon attaining an undue or excessive speed, and it is obvious that this result may be accomplished in many specifically different ways. in one form of retarding apparatus an electro dynamic brake is included, this brake being inshunt circuit across the armature. This shunt circuit is completed automatically upon undue or excessive speed developed by themotor or by the current generated by the motor when it is run as a. generator. I have shown a resistance 79 in Figs. 2, 3 and i connected on oneside to the contact 78 and on the other side through conductor 76 to a contact 66. The cooperating contact 88 is connected through wire 75 to contact 7?. This shunt circuit is normally open between the contacts 66 and 68. Any suitable means may be used, such, for instance, as the magnet- .80 (Fig. 2) arranged to be properly and suitably energized when the motouattains an undue or excessive speed, or becomes a generator, to close the circuit between the contacts 66 and 68. The resistance 79 when its circuit is closed thus forms in effect anelectro-dynamic brake, and its tendency is to slow down the motor.

In Figs. 3 and 4t, magnets 60 and 60,

respectively, control the circuits for the re} sistance 79.

The brake magnet 123 is controlled by a switch operated by the magnet 60 (Figs' 1 and 2 and a) to open the circuit of the brake magnet coil and effect the application of the mechanical brake to stop the motor when the same operates at an excessive speed. If desired, the brake 123 may be controlled only Fig. 3.

by the manual switch'lO as shown in In Figs. 2, 3 and 4 is shown an extra shunt field winding 103 which is connected in circult to automatically strengthen the magnetic field of the motor when the electrodynamic brake circuit is closed. If desired, there may be included in the extra shunt field circuit a resistance 105. The contact (37 is normally separated. from a cooperating contact 69 which is connected through conductor 74 to conductor 51, and hence when this circuit is closed through contacts 67, (39 the auxiliary shunt field circuit is established. The contacts (37, (it) may be brought. into engagement with each other by the magnet 60 when an undue or excessive speed of the motor is attained.

If desired, the methods above described of applying an elcctro-dynamic brake and of strengthening the magnetic field of the motor may be c mbined in their action, or may be carried out atthe same time, as, for in stance, by connecting both contacts 66 and (37 through insulation 70, and a rod 7 2 with the plunger 71 of magnet (30, any suitable arrangement being employed to maintain the contacts 66, 67 normally separated from their respective cooperating contacts 68, 69. For instance, this result may be accomplished by a spring 64: secured at one end to a fixed point- 65 and connected at its other end to the rod 72, the tension of said spring operating to normally maintainthe contacts 66 and 67 out of engagement with the contacts 68 and 69 until the magnet 60 becomes sufficiently energized to overcome such ten- S10I1.

In Fig. 1 the switch controlled by the magnet 60 is in the main conductor or motor circuit. In this case the energization of the magnet 60 in a manner hereinafter described will break the motor circuit by separating the contacts 66 and 67', respectively, from the contacts 68 and 69. It will also be observed that when the switch 10 is closed and the motor circuit is closed, the brake magnet 123 will receive current across the mains. Upon the opening of the switch controlled by the magnet 60, however, not only the motor circuit will become interrupted, but also the circuit of the brake magnet 123, for the reason that the conductor 16 is connected to the contact 66 or 67 Therefore, when the circuit-breaker is in open position, one terminal of the brake magnet is entirely isolated andthe latter therefore cannot possibly receive any current even from the motor acting as a generator.

In Fig' 2 when the motor speed becomes excessive, not only is "the electro-dynamic brake applied and the field of the motor strengthened, but the motor circuit is also interrupted. This may be done in successive order. When the motor circuit is interrupted the circuit of the brake magnet is also interrupted, and one of its terminals isolated. The result, therefore, is that if the magnets 60 and 60 operate successively, the motor will first be slowed down and then be brought to a positive stop automatically by the cutting off of the current from the motor and from the brake magnet.

In Fig. 3 the magnet 60 operates a switch to effect a strong electro-dynamic braking eflect to slow down the motor, which may also bring the motor to a stop, particularly if the load is not too great or is nearly balanced. To positively stop the motor, however, and to hold the same in stationary position, the opening of the manual switch 10 is relied upon to cut off the current from the brake magnet 123. v

In Fig. 1 the magnet 60 is provided with oppositely wound coils 62 and 53. In Fig. 2 the magnet 60 is also provided with oppositely wound coils G2 and 53. The magnets 60 and 60"may therefore each be termed a doubly wound magnet or a differential magnet. In Fig. 1 the winding 53' is arranged to be included in series with the motor armature, while the winding 62 is connected through the conductors 61 and 63 in a shunt circuit around the motor armature, provided the reversing switch is closed and the switch controlled by the magnet 60 is closed. Under these conditions it will be observed that the energizing effect of the windings of the magnets tends to neutralize each other. The energizing effect of the coil (32 will vary with the variation of potential across the motor armature, since said coil is connected directly to the armature brushes when the motor circuit is closed through the reversing switch and the switch controlled by the magnet 60, and the energizing effect of the coil 53 will vary with the current through the armature, and consequently when the potential across the brushes sufliciently increases, due to excessive speed, the overbalancing or neutralizing effect of the coil 53- is overcome and the magnet 60 will become sufliciently energized to accomplish the objects and purposes set forth. In other words, the coils 53 and 62 tend to neutralize each other, and the magnet comprising said coils becomes sufiiciently strong to operate its switch to open the motor circuit only when the difi'erence in the strengths of these coils becomes sufficiently great. Ordinarily at the same time that the coils 62 strengthens, the coil 53' weakens, thus increasing the differential action of the entire magnet. In case the motor becomes a generator so that it sends current back into the line, the flow of current through the coil 53' will coincide in direction with that through coil 62, and the same results will be secured.

The operation of the arrangementshown in Fig. 1 may be explained as follows: Let it be assumed that the switch lever 12 is moved into engagement with the contact 13 contact 67 will engage the contact 69,

so that a circuit will be established from the positive main 7, through conductor 16, lever 12, contact 13, conductor 18, solenoid 91, wire 95 to the negative main 5. The resulting energization of the left-hand magnet as viewed in Fig. 1 results in rocking the lever 80 to the left, thereupon completing the motor circuit as follows: from the positive main 7 to and through the contacts 69, 67, 66, 68, conductor 7, contact 85, contact strip 83, contact 86, conductor 25, brush 23,- armature 21, brush 22, conductor 26, contact 87, contact strip 82, contact 56, conductor 54, coil 53,-conductor 51, series field, coils 50, resistance 40, conductor 41 to the negative main 5. lhe shunt field circuit is completed from the positive main 7 through conductor 102, shunt field winding 100, conductor 101-, and conductor 41 to the negative main 5. The motor can now start, the subsequent operations being automatic. As the motor accelerates, the sectional resistance i0 and the series field coils 50 are gradually cut out, circuits being successively completed through the conductors 13, 4 1, 4:5 and 42.. Should the motor attain an undue or excessive speed and thereby develop an increase of potential, the magnet becomes sufiiciently energized to open the switch 130,

thereby cutting off the current from the motor which Wlll thereupon be slowed down and stopped, particularly when the brake is applied mechanically to the brake pulley on the motor shaft, due to the deenergization of the brake magnet 123. This is provided for in Fig. 1 by connecting the conductor 16 the cross-piece of the switch 130 so that when the latter is opened one terminal of the brake magnet is isolated, therefore by no possibilitycan the latter receive current even from the motor acting as a generator. In Fig. 2, assuming that the motor has been started by noving the switch lever 80 to the left, when the motor an an due or excessive speed or becomes a genboth the magnets 60 and 60 will he tiGtl to eftect a stepping the motor, or they may be so wound that they will act successively. i 7 hen the magnet 60 pu .tiS the insulating cross-piece Y0 downwardly against the action of the spring 64, the contact 66 will engage the contact 68 and thp In shunt circuit is then completed around the armature through the resistance 79. An extra field circuit is alsoclosed including. the windings 103 and the resistance 105. Upon the proper energization of the magnet 60 the main line or motor armature circuit is broken to cut off current from the motor. Upon the opening of the switch 130, current is cut 03 also from thebrake magnet 123. If the magnets 60 and 60 operate successively, the electric-dynamic brake circuit, assisted by the increased strength of field, may retard the motorto such an extent as to stop the same, or nearly so. Then upon the operation of the switch 130 the mechanical brake is applied to positively stop the motor and hold the same from rotating. I

I have traced the circuits when the contact lever 12 is moved onto the contact 13 so as to effect, theenergization of the solenoid 91. When said contact lever 12 is moved in the opposite direction onto the contactl i, the solenoid 92 receives current to rock the-lever 83 toward the right to cause a reversal of current through the motor armature, and thus reverse the direction of rotation of the motor.

In Fig. 2 the coils 53 and 53 are connected in series with each other in the armature circuit between the conductors 54 and 51 when the reversing switch is closed in either direction. At this time also thecoils 62 and 62' are connected in series with each other in a circuit including the conductors 61 and 63, which circuit is in shunt to the motor armature.

In Fig. 3 only one coil 62 is relied upon to operate a switch to close the electro-dynamic brake circuit,.and, if desired, also the extra fieldcircuit. It is evident that this magnet may operate a switch similar to that designated 130 in Fig. 2 torcut off the current from the motor. In Fig. 3 the coil62 is connected directly across the motor armature by means of the conductors 27' and 28, so that when the speed of the motor becomes excessive and the counter-electro-motive force reaches a predetermined value, sullicientcurrent is shunted through the coil 62" to' close the multiple switch 131.

In Figs. 1, 2 and 5 the cells 62 and 62 are connected across the armature outside of the reversing switch, so that the direction of flow of the current in these coils is always the same, regardless of reversals of current through the motor armature. The same is true with regard to the series coils 53 and 53, so that the direction of current through. the d crent coils will always maintain the proper relation. In Fig. tne connections are different. Here the terminals of the coils 62, 62 are connected by the conductors 27, 28 directly tothe armature brushes between the armature and the reversing switch, so that the direction of currentthrough the coils 62, 62' is reversed whenever the current through the motor is reversed. Also the series coils 53, 53 are connected int-he armature circuit between the brush 22'and the reversing switch so that the direction of current through these coils will likewise be reversed when the currentthrough the motor is reversed. Except as just noted the arrangement in Fig. 4 is substantially the same as in Fig. 2.' Thus the directions or current in the various coils will maintain the proper relation, whether the connections are as illustrated in Fig. 4 or as in Figs. 1, 2 and 5. The arrangement in Fig. 4; permits the magnets 60 and .60 to operate independently of the reversing switch and thus maintain the electro-dynamic brake circuit closed and the extra field circuit closed, even though the reversing switch is open. This is also true with respect to Fig. 3 where the single coil 62" connected directly across the armature closes the elcctro-dynamic brake circuit and the extra field circuit independently. of the position of the reversing switch. It should be noted that the shunt field circuit is connected directly across the mains, and therefore permanently energized so long as potentiiil remains on the line, or the positive and negative leads are connected to a suitable source of electric power. For instance, in Fig. 3 current will flow through the shunt field winding 102 whether the reversing switch is closed or open, and if the switch 131 is closed the extra field winding 103 will also receive current. Therefore when the motor is driven by momentum and the switch 131 is closed, an electro-dynamic braking effect is caused by the generation of current through the resistance 79. It should be observed, however, that such retarding effect would be of only short duration when the reversing switch is open, for the reason that the manual switch being opened cuts oil the current from the brake magnet to cause the mechanical brake to be applied.

In Fig. 5 I have shown a doubly wound or differentially acting magnet 60" com-- prising a series coil 53 and a shunt coil 62. These coils are wound so as tooppose each other, and at normal speed of the motor the diiferential action between the two coils on the plunger 71 is not sufficient. to open the switch 130, but when the speed of the motor becomes excessive or reaches a predetermined value, or the motor acts as .a generator, the coil 62 will overcome the action of the coil 53 and the core 71 will be drawn downwardly to open the switch 130 and thus break the circult throu h the con-- ductors 109, 110, solenoid 111 an conductor 112. In this instance a main line switch 132 is interposed between the positive and negative mains and the switch 130. This mam line switch is controlled b the potential magnet comprising the so enoid 111 and plunger 118. The latter is connected by therod 117 to the insulating cross-piece 116. which in turn carries the contacts 108 and 113. Normally the compression spring 115 presses down on the insulating bar 116, but the latter may be moved upwardly manually by means of the handle 119 so that the contact 103 will en age the contact 107 and the contact 113 will engage the contact 114.,

The potential magnet Will thus be placed 7 tor and efi'ect the application of the mechanical brake illustrated at the upper lefthand portion of Fig. 5. The mechanical brake may be of any type desired. In this instance I have shown a brake pulley 128, and associated with the sr me the brake levers 126, 126. These brake levers are normally held together against the pulley 128 by means of the spring 127, and when the solenoid 123 receives current the core 125 will be lifted against the action of the spring 127 to release the brake shoes.

The operation of the apparatus illustrated in Fig. 5 is as follows:' Vi hen the handle 11 of the switch 10, which may be in an elevator car for instance, is moved to the right or left, the motor circuit is closed and the motor is accelerated to full speed, provided the brake apparatus 120 is first operated. This is accomplished by the contacts 121, 121 in the switch 10 which are engaged by the lever 12 to close a circuit which may be traced from the positive main through the contacts 107, 107, wire 109, contacts 68, 66', wires 16, 122, magnet 123, wire 124;, and contacts 113 and 114 to the negative main. Now, when the motor speed exceeds a predetermined value or becomes a generator, the switch 130 will be opened, and thereforecurrent immediately cut ofi from the brake magnet 123. This will cause the brake apparatus 120 to be applied to positively stop the motor. When the switch 130 is opened, the potential switch will also be opened to cut off the current entirely from all the motor circuits. In such case the main line switch 132 must be closed manually before the motor can again be started.

Having now set forth the objects and nature of my invention, and various constructions, and arrangements for accomplishmg such objects, and without limiting myself to any of the details, what I claim as new and useful and of my own invention, and desire to have rotected by Letters Patent of the United gtates, is

1. The combination with a motor, of controlling apparatus therefor, a differential re lay, and means controlled by said relay for -efi'ecting a positive stop of said motor when the same acts as a generator or attains an undue speed.

2. The combination with a. motor, of a main line switch therefor, a brake magnet, a doubly wound magnet, and means whereby said doubly wound magnet effects the opendetermined value ing of the main line switch and the oleenergization of said brake magnet when the motor acts as a generator or runs at an excessive speed.

3. The combination with an electric motor, of a main line switch and controlling apparatus for said motor, a brake magnet, a difierentially wound magnet associated with said switch and having one winding connected in series with the motor armature, and having the other winding connected across the motor armature, means for maintainin said switch in closed position during norma operation of the motor, and means controlled by said differential magnet for etlecting the opening of the main line switch and the delnergization of the brake magnet when the motor attains an encessivespeed.

4. The combination with an electric motor, of a doubly wound magnet having one winding connected directly across the motor armature, and the other winding arranged to be connected in series with the motor armature, and electro-mechanical means controlled by said electro-inagnet for efiecting the stopping of the motor when the speed of the latter become-s excessive or when said motor acts as a generator.

5. The combination with an electric motor, of controlling apparatus therefor, a doubly wound magnet, and electrical devices controlled by said magnet for efiecting a positive stop of the motor when the speed of the latter becomes excessive or when said motor acts as a generator. 7

6. The combination with an electric motor, of controlling apparatus therefor, a difierentially wound magnet having one winding dependent upon armature potential and the other upon armature current and normally receiving opposing currents, and means mechanically disconnected from but controlled by said magnet for etlecting a positive stop of the motor.

7. The combination with a motor, of con trolling apparatus therefor, an electric switch for closing the circuit to the motor, and a ditterential magnet having its windings connected to the motor and controlled thereby and arranged to control said switch to efiect the interruption of current to the motor when the speed of the latter becomes excessive or when said motor acts as a generator.

8. The combination with a motor, of a reversing switch, a brake magnet, a switch in the brake magnet circuit, and a difiierential el'ectromagnet havin windings connected to normally receive opposing currents for operating said last named switch whenthe potential across the armature exceeds a pre- 9. The combinaieolil with a motor, of a reversing switch a brake magnet,-a switch controlling the brake magnet circuit, and an no'asgre electromagnet comprising windings in parallel and'in series respectively with the motor armature for operating said last named switch when the potential across the armature exceeds a predetermined value.

10. The combination with a motor, of

brake apparatus therefor comprising a brake magnet, a switch for controlling the brake magnet circuit, and a differential magnet for operating said switch upon the speed or the motor exceeding a predetermined value.

11. The combination with a motor, of a difilerentially wound magnet having its windings connected in series and parallel, respectively, with the motor armature and receiving opposing currents the normal operation of the motor, s switch operated by said magnet, and a brake magnet controlled by said switch.

12. The combination with an electric inotor, of adoubly wound magnet having one winding connected permanently across the motorarmature, and the other winding in series with the motor armature, and means controlled by said magnet for efiecting the retardation or stopping of the motor.

13. The combination with an electric motor, of a reversing switch for the motor, a differential relay having its windings both connected between the motor armature and respectively, with the motor armature, and

means operated by said relay for controlling the speed or" the motor.

14. The combination with a motor, of a supply circuit therefor, a brake magnet, a switch in said supply and brake magnet an cuits, an additional switch arranged to con trol the field strength of the motor and a resistance in a circuit around the armaturebrushes, and difierential magnets associated with both of said switches and arranged connected so that the operation of switches will efiect a slow down and stopping of the motor when the speed ot' the latter exceeds a predetermined 15, The combination a means dependent upon the speed of the mo tor for efiecting a retardation of e v additional means for stopping the motor whenever the speed of the latter exceeds a predetermined limit, and di'derential magnet windings associated with both 9:. s id means, substantially as described.

16. The combination with a motor, or" brake and circuit therefor, a normally open circuit in shunt to the motor armature, electrically operated switches for controlling said brake and shunt circuits, and means for efiecting the operation of said switches one before the other, said means madeoperative upon undue or excessive speed of the motor and comprising difierential magnet windings.

tor, of means entirely electrical for reducing the speed of the motor, means for positively stopping; the motor, and differential magnet windings associated with and arranged to operate said speed reducing and stopping means upon undue speeds of the motor.

18. The combination with an electric motor, of a main line switch, a brake, a circuit 'for said brake controlled by said switch,

mechanical means for holding said main line switch in closed position, a diiierentially wound magnet having one winding connected across the motor armature and the other in series therewith. and means operated by said magnet for opening said niain line switch.

19. The combination with an electric motor, of a main line switch, a brake, a circuit for said brake controlled by said switch, means for operating the switch, a doubly wound magnethaving one winding connected across the motorarmature and the other winding in series with the motor armature, and means operated by said magnet when the motor speed exceeds a predetermined value for effecting the opening of the main line switch.

20. The combination with an electric m0- tor, of an electro-dynamic brake circuit for the motor, a field circuit for the motor, a switch in said circuits, means for holding said switch open during the normal operation of the motor, an elect-romagnet for closing the said switch, and a circuit for the magnet. winding permanently connected in parallel with the motor armature.

terminals connected betweelrthe armature and the reversing switch.

In testimony whereof, I have signed my name to this specification in the presence of two subscribing witnesses.

JOHN D. IHLDER. Witnesses:

CHAS. M. Nissan, JAMES G. BE'I'HELL. 

